Comments on: I wanna be ablatedhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/
Wed, 13 Dec 2017 21:32:13 +0000hourly1https://wordpress.org/?v=4.9.1By: zbicyclisthttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465921
Sat, 15 Apr 2017 13:18:55 +0000http://andrewgelman.com/?p=33354#comment-465921BMI is a “first cut” variable based on height and weight measures that can be easily obtained in a doctor’s office or asked on a survey. They are even on my driver’s license. The limitations are well known (e.g. Michael Jordan was not really obese in his playing days, just very well muscled). But ease and reliability of measurement (where weight is not self-reported) make the measure useful.
]]>By: Martha (Smith)http://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465801
Sat, 15 Apr 2017 03:10:31 +0000http://andrewgelman.com/?p=33354#comment-465801BMI stands for Body Mass Index. It is the ratio of body mass by height (adjusted to give standard units). It is intended as a rough measure of degree of obesity or un underweight. Medical decisions also need to consider other relevant factors, depending on the purpose. These factors might include sex, age, and body type (e.g., fat distribution, muscle mass)
]]>By: Carolhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465656
Fri, 14 Apr 2017 17:02:34 +0000http://andrewgelman.com/?p=33354#comment-465656Terry: I agree that these seems to be amazingly clean and strong results. But I have no expertise in this topic.
]]>By: Anonymous2http://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465653
Fri, 14 Apr 2017 16:52:51 +0000http://andrewgelman.com/?p=33354#comment-465653I have no idea what my BMI is, so I just entered my height and weight into one of those online calculators. I was quite surprised to see that BMI is based on height and weight only. Why is sex not considered? Or age??
]]>By: Terryhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465647
Fri, 14 Apr 2017 16:25:51 +0000http://andrewgelman.com/?p=33354#comment-465647The causal language in the article seems pretty aggressive. It claims or implicitly assumes one-way causation from weight-loss to 22 measures of health including Atrial Fibrillation (AF). It looks like their Table 2 could be restructured to make any of the 22 health measures the independent variable and to “show” that any of the 22 health measures “causes” improvements in the other health measures.

My intuition (unsupported by any medical training) is that AF improvement is the primary driver of weight loss, i.e., that causation runs in the opposite direction to that assumed by the authors. It seems reasonable that when heart problems go away, subjects tend to lose weight because they are more active, they eat better, and their metabolism is healthier than when they were sick.

Particularly noteworthy is that ALL health measures, including AF symptoms, improved for all the weight loss groups, including the group that lost little or no weight: Global Well-Being went from 2.5 to 5.7 for the <3% Weight-Loss Group. This suggests there is substantial mean reversion in AF symptoms that is independent of weight loss.

A less aggressive description of the results would be pretty boring, though. It might be something like this:
“We studied 355 subjects with Atrial Fibrillation symptoms over a period of 4 years. On average, subjects’ health improved markedly on 22 measures of health over the 4 year period. Health measure included …. Subjects’ health improvement was positively correlated with weight loss, although health improved substantially for all weight-loss groups, even for the group that lost little or no weight.”

The statistical results are also astonishingly strong. Every one of the 22 p-value in the rightmost column of Table 2 is <0.001. It is particularly startling that each of the 4 measures of cholesterol changes significantly, and in the “better” direction. Further, every single one of the 22 health measures (except one) shows monotonic improvement across the 3 weight loss groups.

]]>By: mpledgerhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465342
Thu, 13 Apr 2017 21:38:05 +0000http://andrewgelman.com/?p=33354#comment-465342Maybe because they think the relationships are likely to be non-linear and they have outliers in the weight-loss values that make splines non-starters.
]]>By: Martha (Smith)http://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465333
Thu, 13 Apr 2017 21:07:04 +0000http://andrewgelman.com/?p=33354#comment-465333+2
]]>By: Jonathanhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465315
Thu, 13 Apr 2017 19:51:15 +0000http://andrewgelman.com/?p=33354#comment-465315BTW, kudos for the Ramones reference.
]]>By: Jonathanhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465303
Thu, 13 Apr 2017 18:56:07 +0000http://andrewgelman.com/?p=33354#comment-465303I liked the study or, rather it fit with my prior that Afib tends to be a progressive condition, like other heart ills, and that it will tend to worsen without intervention (and sometimes despite that) and among the most sensible interventions are generally diet and exercise. I particularly noted the section on cardiac improvements; meaningful weight loss reduced ventricle volume and reduced the thickening of the the interior heart wall, which are both very good things. The correlative model is fairly compelling and I think it’s case is made stronger by the relative good effects tending to disappear and even to reverse as weight remained relatively stable (especially when fluctuation is involved) because this suggests there is an underlying condition which manifests as Afib AND that maintaining or fluctuating around typical weight may allow the condition to progress. Beyond that, I’d have a million questions: does reason for BMI matter (the old Arnold is obese quandary)? Is exercise without weight loss better? Worse? How much does fluctuation matter – and does it only matter when it …? And so on. And if you are fit, does weight loss make the condition better or worse or does it not matter? And again exercise is …?

As for me, I want a condition in which the prescription is to relax and enjoy myself and then see whether that motivates me to improve my condition. Instead, I get this bleep.

]]>By: Patrick Linehanhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465294
Thu, 13 Apr 2017 18:26:44 +0000http://andrewgelman.com/?p=33354#comment-465294So the major confounder is that the type of people that can lose weight easily are also the type of people who are generally healthier and who will have better health outcomes than those people who can not lose weight easily. No surprise there at all. Also, no causal relationship between this specific intervention and the outcome of better health.
]]>By: Bobhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465291
Thu, 13 Apr 2017 18:19:16 +0000http://andrewgelman.com/?p=33354#comment-465291Just looking at the >10% group.

They went from mean AF frequency 7 to AF frequency 3 (this is a scale of 1-10) and a duration of 7 to 4.

A change of that magnitude will make a big difference in one’s quality of life!

Mean global well being went from 2.7 to 8.1—a delta of 5.4 on a scale with maximum delta of 9.

My global well being jumped about that much when I had successful cardiac ablation for afib.

Bob

]]>By: Bobhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465287
Thu, 13 Apr 2017 18:13:11 +0000http://andrewgelman.com/?p=33354#comment-465287+1 They had lots of space. On the other hand, they measured lots of variables.
]]>By: LauraKhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465286
Thu, 13 Apr 2017 18:12:30 +0000http://andrewgelman.com/?p=33354#comment-465286+1
]]>By: Nick Menzieshttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465269
Thu, 13 Apr 2017 17:01:09 +0000http://andrewgelman.com/?p=33354#comment-465269Aside from any multiple testing concerns, the paper uses some pretty causal language to describe the correlations estimated, and this issue (omitted variables bias / confounding) really doesn’t get any play in the limitations section. I am not the subject matter expert to know whether the factors that lead to weight loss might be independently associated with the outcomes they are interested in, but seems plausible.
]]>By: Clarkhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465268
Thu, 13 Apr 2017 16:59:28 +0000http://andrewgelman.com/?p=33354#comment-465268My greater concern is arbitrary categorization boundaries. An argument can be made to split at (sometimes approximate) quartiles or tertiles for clarity, likewise sometimes there are informed reasons for particular boundaries. Alternatively, you can model on a continuum and use the model to estimate where on the continuum important differences occur.
]]>By: Nick Menzieshttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465266
Thu, 13 Apr 2017 16:50:41 +0000http://andrewgelman.com/?p=33354#comment-465266I understand this motivation, but the need for easy heuristics need to be baked into the analysis?

It would seem one can have one’s cake and eat it too — analyse the data in the most appropriate format, then use those results to construct the decision aid.

]]>By: David Manheimhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465260
Thu, 13 Apr 2017 16:28:46 +0000http://andrewgelman.com/?p=33354#comment-465260In clinical settings, especially where rapid decisions are needed, simplified categories are easier to apply. That can save lives, since doctors are frequently overloaded with things they need to have memorized and other complex clinical guidelines already.

Of course, this should be fixed – and Atul Gawande had written about using checklists to help solve this, in part. But until problem is fixed, simple binary/categorical guidelines are not only ok, but I’d argue better than the more accurate analyses that statisticians would prefer.

]]>By: Matthttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465255
Thu, 13 Apr 2017 16:23:30 +0000http://andrewgelman.com/?p=33354#comment-465255I’m in a different field (human-computer interaction), but familiarity with ANOVA is an explanation that rings true to me. Analysis step 1 is bash your face against the data until you can run an ANOVA on it. When all you have is a hammer…
]]>By: Anoneuoidhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465252
Thu, 13 Apr 2017 16:19:20 +0000http://andrewgelman.com/?p=33354#comment-465252How could a table of anova results be more understandable than a scatterplot of, eg, “% weightloss” vs “atrial fibrillation frequency”? If true, their mindset must be completely foreign to me. That would actually explain a lot about how difficult it is to communicate with them though.
]]>By: Andrewhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465251
Thu, 13 Apr 2017 16:17:45 +0000http://andrewgelman.com/?p=33354#comment-465251Anon, Carol, Clark:

From the standpoint of statistical efficiency, it’s a lot better to use 3 categories than 2. David Park and I discuss in this paper, “Splitting a predictor at the upper quarter or third and the lower quarter or third.”

]]>By: Clarkhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465248
Thu, 13 Apr 2017 16:12:25 +0000http://andrewgelman.com/?p=33354#comment-465248MDs love these arbitrary categories — I think partially because they see them in so many papers and professional guidelines, and also because it facilitates them making quick decisions for patient treatment as opposed to thinking more deeply about changes over a continuum. I’d like to think that it is not driven by p-hacking, though I know that happens too.

I’ve had good success pushing back on this, pointing-out the arbitrariness of the categories, and helping them to interpret results on a continuum and communicate it to others. The important thing is to not just take the data they bring and analyze uncritically.

]]>By: Carolhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465247
Thu, 13 Apr 2017 16:06:54 +0000http://andrewgelman.com/?p=33354#comment-465247Anoneuoid: Perhaps because they are more familiar with anova than regression? Or perhaps they think the results presented in tables like these will be more understandable to the readers (who might include non-academic physicians as well as academics)?
]]>By: Carolhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465238
Thu, 13 Apr 2017 15:43:29 +0000http://andrewgelman.com/?p=33354#comment-465238Those increases in “global well-being” seem enormous. Pre and post means on a scale of 1 to 10 for the three groups:
2.7 -> 8.1; 2.4 -> 6.1; 2.5 -> 5.7.
]]>By: zbicyclisthttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465228
Thu, 13 Apr 2017 14:57:28 +0000http://andrewgelman.com/?p=33354#comment-465228I’d like it to be right, as would the cardiologists. There tends to be less critical scrutiny of results we’d like to believe are correct.
]]>By: Anoneuoidhttp://andrewgelman.com/2017/04/13/i-wanna-be-ablated/#comment-465219
Thu, 13 Apr 2017 14:14:02 +0000http://andrewgelman.com/?p=33354#comment-465219

weight loss (>=10%, 3-9%, <3%)

Why do medical researchers/journals insist on turning everything into categories like this? I have still never gotten an answer. Is it really as simple as I suspect: Because that’s a major p-hacking tool?